The present invention relates generally to an apparatus for setting the ignition timing of an internal combustion engine, and more particularly, to a tool for setting the ignition timing of Harley Davidson(trademark)-type motorcycle engines and similar engines while the engine is running.
The conventional method of setting the ignition timing of many models of Harley Davidson(trademark) motorcycles is time-consuming and difficult. In these models, the information needed to adjust the timing of the motorcycle engine is on the opposite side of the motorcycle from the ignition unit where timing is to be adjusted. There are indicators for piston top dead centre (TDC) and ignition timing marked on the flywheel. These indicators are viewable through a small observation port on one side of the engine, the timing indicator side. An ignition unit is mounted on the opposite side of the engine, the timing adjustment side. The ignition unit includes a circuit breaker assembly having a mechanical points mechanism and advance unit for adjusting the ignition timing.
The conventional steps for adjusting the timing of such Harley Davidson(trademark) motorcycle engines while the engine is running, are as follows: a mechanic first determines the location of TDC of the piston compression stroke relative to the rotational position of the driveshaft; this can be accomplished by removing a sparkplug and noting when the piston reaches the TDC position. Or, the mechanic may, shine a light through the observation port onto the flywheel that is visible through the port to observe a TDC mark on that flywheel. Then, the mechanic determines the degree of spark advance relative to TDC, i.e. where the spark plug is firing relative to the position of the piston (measured in degrees of rotation where TDC is zero) as follows: a standard inductive pickup communicative with the spark plug measures the spark timing, then sets a strobe timing light frequency in time with the spark timing; when the strobe light is aimed through the observation port, it illuminates an ignition timing mark indicative of the degree of spark advance. Then, the mechanic must move to the other side of the motorcycle, i.e. the timing adjustment side, to adjust the points mechanism and advance unit to alter the spark timing (and consequently, the strobe frequency), then returns to the timing indicator side of the motorcycle to view the new timing mark. Typically, the mechanic must move from one side of the motorcycle to the other side several times to calibrate the ignition timing to the selected degree of accuracy. Obtaining accurate timing is a tedious and time-consuming process of trial and error. Because the engine is running, the mechanic is sprayed with oil coming out of the observation port every time he observes the timing mark. This method of setting the timing is inconvenient and messy.
The prior art of which the inventor is aware includes a conversion kit which replaces the points plate and advance unit of a stock ignition system with a modified points plate and modified advance unit that permits observation of a marked disk that is mounted upon the circuit breaker cam so that it rotates with the cam. As the points plate and advance unit contain a number of precision parts, the modified points plate and advance unit is relatively complex and expensive to manufacture. Therefore, it is not particularly cost-effective to replace the original functional points plate and advance unit for the purpose adjusting ignition timing.
A simple-to-use, inexpensive tool for adjusting ignition timing of Harley-Davidson and similar motorcycle engines such as SandS and Merch Performance from the ignition unit/circuit breaker side of the engine without replacing the stock circuit breaker points plate and advance unit may be preferred over the prior art by those owners of such motorcycles who prefer to set ignition timing themselves and to use stock parts for cost or availability reasons.
The present invention is directed in one aspect to providing an auxiliary ignition timing display tool (hereinafter xe2x80x9ctiming display toolxe2x80x9d) for adjusting the ignition timing of a Harley-Davidson motorcycle engine or similar engine using a strobe timing light. The timing display tool includes (1) a replacement pointer cam bolt threaded at a distal end to match the stock circuit breaker cam bolt, (2) a pointer indicator attached to the proximal end of the pointer cam bolt, (3) an ignition timing measuring plate having spaced timing marks indicating in degrees the spark position relative to TDC, and attachable to the gear cover of the engine, and (4) measuring plate fastening means for fastening the measuring plate to the engine.
To install the timing display tool, a number of parts from the engine must be temporarily removed. A circuit breaker cover and gasket is removed to expose the inside of the ignition unit and provide access to an engine timing setting adjustment device, such as a points mechanism and advance unit. A circuit breaker cam assembly bolt is removed and replaced with the pointer cam bolt, and gear cover screws are removed and replaced with the measuring plate fastening means. The measuring plate is then installed on the fastening means so that the measuring plate is positioned in front of a front rim of an engine gear cover. Then, the pointer indicator is installed on the proximal end of the pointer cam bolt.
The engine is turned on and a standard strobe timing light communicates with the ignition system to match the strobe frequency with the spark firing frequency of the engine. The strobe light is then shone on to the measuring plate to illuminate the pointer at a timing mark on the measuring plate corresponding to the spark position. The engine timing setting adjustment device may then be adjusted in the conventional manner to alter the ignition timing until the pointer points to the desired timing mark.
The prior art of which the inventor is aware includes a conversion kit which replaces the points plate and advance unit of a stock ignition system with a modified points plate and modified advance unit that permits observation of a marked disk that is mounted upon the circuit breaker cam so that it rotates with the cam. As the points plate and advance unit contain a number of precision parts, the modified points plate and advance device which when installed is operatively coupled to the ignition unit and indicates the degree of spark advance or retard relative to an engine top dead center position and provides a display of the indication viewable on the same side of the engine as that on which the engine timing setting adjustment device is located, i.e. the timing adjustment side. The display device is removably attachable to the engine housing. The timing display tool kit also includes a plurality of fasteners for releasably fastening the display device to the engine housing and positioning the display device in a preselected position suitable for coupling of the display device to the ignition unit. The display device in conjunction with the strobe timing light set at the spark firing frequency of the engine are operable to provide an indication of the ignition timing of the engine while the engine is running. If the engine has a gear cover, the display device may be removably attached to the gear cover; the fasteners when installed releasably fasten the display device to the gear cover.